ODE: A Data Sampling Method for Practical Federated Learning with Streaming Data and Limited Buffer

Machine learning models have been deployed in mobile networks to deal with the data from different layers to enable automated network management and intelligence on devices. To overcome high communication cost and severe privacy concerns of centralized machine learning, Federated Learning (FL) has been proposed to achieve distributed machine learning among networked devices. While the computation and communication limitation has been widely studied in FL, the impact of on-device storage on the performance of FL is still not explored. Without an efficient and effective data selection policy to filter the abundant streaming data on devices, classical FL can suffer from much longer model training time (more than $4\times$) and significant inference accuracy reduction (more than $7\%$), observed in our experiments. In this work, we take the first step to consider the online data selection for FL with limited on-device storage. We first define a new data valuation metric for data selection in FL: the projection of local gradient over an on-device data sample onto the global gradient over the data from all devices. We further design \textbf{ODE}, a framework of \textbf{O}nline \textbf{D}ata s\textbf{E}lection for FL, to coordinate networked devices to store valuable data samples collaboratively, with theoretical guarantees for speeding up model convergence and enhancing final model accuracy, simultaneously. Experimental results on one industrial task (mobile network traffic classification) and three public tasks (synthetic task, image classification, human activity recognition) show the remarkable advantages of ODE over the state-of-the-art approaches. Particularly, on the industrial dataset, ODE achieves as high as $2.5\times$ speedup of training time and $6\%$ increase in final inference accuracy, and is robust to various factors in the practical environment

QDR-Tree: An Efcient Index Scheme for Complex Spatial Keyword Query

With the popularity of mobile devices and the development of geo-positioning technology, location-based services (LBS) attract much attention and top-k spatial keyword queries become increasingly complex. It is common to see that clients issue a query to find a restaurant serving pizza and steak, low in price and noise level particularly. However, most of prior works focused only on the spatial keyword while ignoring these independent numerical attributes. In this paper we demonstrate, for the first time, the Attributes-Aware Spatial Keyword Query (ASKQ), and devise a two-layer hybrid index structure called Quad-cluster Dual-filtering R-Tree (QDR-Tree). In the keyword cluster layer, a Quad-Cluster Tree (QC-Tree) is built based on the hierarchical clustering algorithm using kernel k-means to classify keywords. In the spatial layer, for each leaf node of the QC-Tree, we attach a Dual-Filtering R-Tree (DR-Tree) with two filtering algorithms, namely, keyword bitmap-based and attributes skyline-based filtering. Accordingly, efficient query processing algorithms are proposed. Through theoretical analysis, we have verified the optimization both in processing time and space consumption. Finally, massive experiments with real-data demonstrate the efficiency and effectiveness of QDR-Tree